PSI - Issue 42

9

Toru Yagi et al. / Procedia Structural Integrity 42 (2022) 702–713 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

710

Fig. 3.4 Schematic image of fracture surface with local brittle zone

The important assumption for interpretation of the model calculation results is the difference in minimum crack velocity based on the theory of plastic strain. Since the plastic strain is big in bending mode, the minimum crack velocity will be close to static solution while one of tensile mode is around 400m/s since its plastic strain is small based on the previous study. The minimum crack velocity of bending mode is set as 10m/s in this study. Fig. 3.5 is the schematic image of the arrest of the pop-in crack.

Fig. 3.5 Pop-in crack arrest mechanism

The results of this new model are shown in Fig. 3.6. The green line represents the section notch specimens since the width of NRL-S is 2mm in the experiment, and the blue line represents the surface notch specimens of the experiment. This model can explain the actual experiment in chapter 2. From this result, it is suggested that the brittle crack is more likely to arrest in bending mode than tensile mode in case of the straight crack shape, but 3D tunnel crack shape effect helps to enhance arrest ability in both modes, bending and tension. And it becomes clear that LBZ width requirement is important for the pop-in crack arrest ability when the judgement condition in standards will be discussed.